1. Technical Field
This disclosure relates to an antenna for use in a radio communication apparatus such as a mobile communication apparatus, and a radio communication apparatus provided with the antenna.
2. Background Art
Patent Documents 1 and 2 disclose antennas for use in plural frequency bands in radio communication apparatuses such as terminal devices (cellular phones) of a cellular phone system. FIG. 1 is a perspective view of the antenna described in Patent Document 1. In FIG. 1, a radiation electrode 12, and non-feeding electrodes 13 and 14 are formed on a top surface of a dielectric base 11. In addition, a ground electrode 15 is formed on substantially the entirety of a bottom surface of the dielectric base 11 so that an excitation conductor 19 does not touch the ground electrode 15. Further, ground conductors 16, 17, and 18, for respectively grounding the radiation electrode 12 and the non-feeding electrodes 13 and 14, are formed on a side surface of the dielectric base 11.
As described above, by forming a radiation electrode, and a plurality of non-feeding electrodes having resonant frequencies close to that of the radiation electrode on the same plane, and combining a plurality of resonances, an antenna having wideband characteristics is realized.
In addition, Patent Document 2 indicates that an antenna having gain in two frequency bands is configured by using a multi-resonance of fundamental wave resonances and harmonic resonances generated by a feeding electrode and a non-feeding electrode. Specifically, by forming spiral slits in the feeding electrode and the non-feeding electrode, a resonant frequency of a harmonic resonance (higher mode) can be set to a desired frequency almost without changing a frequency of a fundamental wave resonance (fundamental mode).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 11-127014
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-8326
As indicated by Patent Document 2, by providing slits on a feeding electrode and a non-feeding electrode, a resonant frequency of a harmonic can be controlled. However, depending on a combination of a resonant frequency of a fundamental wave and a resonant frequency of a harmonic, matching is frequently not established at the resonant frequency of the harmonic. Accordingly, an optimal return loss may not be obtained. In other words, considering capacitive coupling between the feeding electrode and the non-feeding electrode, as the length of the slit formed in each of the feeding electrode and the non-feeding electrode increases, inductance functionality increases and capacitance functionality decreases. Accordingly, the amount of coupling of harmonic resonances between the feeding electrode and the non-feeding electrode is reduced, so that a problem occurs in that a desired gain cannot be obtained since a return loss at a harmonic resonant frequency is large.